1. Field
The embodiments generally relate to material handling systems and, more particularly, to automated storage and retrieval systems.
2. Brief Description of Related Developments
Warehouses for storing case units may generally comprise a series of storage racks that are accessible by transport devices such as, for example, fork lifts, carts and elevators that are movable within aisles between or along the storage racks or by other lifting and transporting devices. These transport devices may be automated or manually driven. Generally, where the case units are stored in multilevel racks, case units are placed on the different levels of the racks with a lifting device on the transport device. Where the case units are stored in racks located on different floors or levels of the storage structure the case units are generally transported between the floors while disposed on the transport devices where the transport devices travel up and down ramps spanning between the floors. In other examples the transport device with the case units disposed thereon are raised and lowered between the floors with an elevator. Generally, the case units carried by the transport devices and stored on the storage racks are contained in carriers, for example storage containers such as trays, totes or shipping cases, or on pallets. Generally, incoming pallets to the warehouse (such as from manufacturers) contain shipping containers (e.g. cases) of the same type of goods. Outgoing pallets leaving the warehouse, for example, to retailers have increasingly been made of what may be referred to as mixed pallets. As may be realized, such mixed pallets are made of shipping containers (e.g. totes or cases such as cartons, etc.) containing different types of goods. For example, one case on the mixed pallet may hold grocery products (soup can, soda cans, etc.) and another case on the same pallet may hold cosmetic or household cleaning or electronic products. Indeed some cases may hold different types of products within a single case. Conventional warehousing systems, including conventional automated warehousing systems do not lend themselves to efficient generation of mixed goods pallets. In addition, storing case units in, for example carriers or on pallets generally does not allow for the retrieval of individual case units within those carriers or pallets without transporting the carriers or pallets to a workstation for manual or automated removal of the individual case units.
It would be advantageous to be able to transport uncontained or unpalletized case units between levels of a storage facility independent of transport device movement between the levels.